IE42269B1 - Improvements in or relating to air-cleaning and ventilating devices - Google Patents

Description

This invention relates to air-cleaning and ventilating devices.

In some known devices, the air in a room is drawn off through an exhaust air grid and preliminary filter, purified in a high efficiency particulate air filter unit (HEPA filter unit) and recycled into the room (air circulation process). In some devices, fresh air is added to the air drawn off from the room, that is to the portion to be recycled, before it passes the HEPA filter unit, while allowing an equivalent portion of the contaminated air to pass into the atmosphere as exhaust, or through a central purification system, again before passage through the HEPA filter unit.

These known devices require considerable constructional arrangements in the room. Ceiling, walls or floor must be provided with appropriate grids for the exhaust air and supplied air. The circulated and the fresh air are purified in central systems where the exhaust air is also purified, which may cause cross-contaminations when more than one room is connected to the system. Transportable small devices have been developed for the air circulation process (cf. git Pachzeitschrift fur das Laboratorium 14, 1970, page 1122) to maintain cleanliness in small areas.

The present invention provides a device for ventilating and cleaning air in a room, comprising a casing having an inlet grid and an outlet grid and two other openings, and a preliminary filter, a blower and a high efficiency parti42269 - 3 culate air filter unit (HEPA filter unit) as hereinafter defined mounted within the casing, the arrangement being such that in operation air enters the device through the inlet grid from the room and through one of the two other openings referred to from the atmosphere outside the room, passes through the preliminary filter, the blower and the HEPA filter unit in that order, and part of the resulting air is circulated through the outlet grid to the room and part is returned .to the atmosphere outside the room through the second opening.

The device of the present invention can be installed in simple manner. It may be used to maintain a clean room as defined in U.S. Federal Standard 209a, the circulated air, the fresh air and the exhaust air being purified by means of an HEPA filter unit, and to ventilate the room.

In the device of the present invention, the first opening of the two other openings referred to may be between the inlet grid and the preliminary filter, and the second of said openings may be between the HEPA filter unit and the outlet grid. Preferably, one or each of these openings is provided with a throttle valve to control the flow of air.

Advantageously, at least one of the grids is constructed as a heat exchanger.

The HEPA filter unit is as defined in paragraph 20.6 on page 11 of U.S. Federal Standard 2O9B, which reads as follows:20.6 High efficiency particulate air(HEPA) filter. A filter as specified in MIL-F-51068 with a minimum efficiency of 99.97 per cent when filtering a dioctylphthalate aerosol having an average particle size of 0.3 micron, as determined by test. The test can be by the homogeneous dioctylphthalate (DOP) method or other equally sensitive method at an airflow of 100 per cent of the rated flow capacity for all size filters and at 20 percent of the rated airflow for sizes 4, 5, and 6. - 4 The invention will now be described in further detail, by way of example only, with reference to the accompanying drawing which is a section through an aircleaning and ventilating device of the invention located in a room to be ventilated, and which also illustrates the pressure conditions in the device.

The device comprises a casing (10) having an air inlet grid (1) at the exhaust air side and an air outlet grid (5) at the clean air side, and, mounted within the casing (10) between the grids (1, 5), a preliminary filter (2) with supporting and holding grids (11), a blower (3) and a HEPA filter unit (4). The space between the inlet grid (1) and the preliminary filter (2) is a suction space (7) provided with an opening (8) with a throttle valve (12), which open15 ing communicates with the atmosphere outside the room. The space between the HEPA filter unit (4) and the air outlet grid (5) is a pressure space (6) which is likewise provided with an opening (9) with a throttle valve (13) and in communication with the atmosphere outside the room.

In operation, air is drawn in from the room via the air inlet grid (1) and from the atmosphere outside the room via the opening (8), into the suction space (7), through the preliminary filter (2) into a further suction space between the filter (2) and the blower (3), through the blower (3)'and· into a pressure space between the blower (3) and the HEPA filter unit (4), through the HEPA filter unit (4), and into the pressure space (6), and air is then returned to thp room via the grid (5) and into the atmosphere outside the room via the opening (9). In the drawing the full line (14) denotes the circulated air, the dashdotted line (15) denotes the fresh air and the dotted line (16) represents the exhaust air.

The HEPA filter unit (4) should be dimensioned in accordance with the amount of air to be treated per unit of time. With a given HEPA filter unit, the air inlet grid (1), the preliminary filter (2) and the air outlet grid (5) 42369 - 5 should be harmonised to one another in such a manner that the absolute value Δρ7 in the suction space (7) is equal to the absolute value Δρ6 in the pressure space (6). The ratio of fresh air; circulated air and of exhaust air: (circulated air+fresh air) is adjusted by the throttle valves (12, 13). If desired or required, one or both of the grids (1, 5) may be constructed as a heat exchanger.

The device of the invention has a simple construction and offers the advantage that one blower and one HEPA filter unit are sufficient for the transport and the purification of three air currents. It can be fitted without special constructional provisions into existing rooms. In principle, the device of the invention can be used for all rooms requiring clean air techniques, especially for venting clean rooms in which infectious substances are handled.

The following Example illustrates the invention.

EXAMPLE A room having a floor area of 20 m and a height of 2.5 m, which was vented in conventional manner by total air exchange with '5 air changes per hour, with two persons working therein each having an emission of 5x10® particles per minute, contained a calculated particle concentration of x 108 fi -=2.4 x 10 particles/m 250 or 2,400 particles/1 of air.

With a Royco particle counter, from 2,000 to 4,000 particles were counted/1 of air.

Without increasing the amount of fresh air supplied, the concentration was reduced to less than 500 particles/1 48389 - 6 of air by the use of the device of the invention.

For the device of the invention, an HEPA filter unit 2 having a surface area of 1.2 m was chosen which permitted air velocities of approximately 0.3 to 0.6 m/sec. With an air speed of 0.5 m/sec, 2,160 m of air were filtered/hr.

Including the above-mentioned amounts of fresh air and 3 exhaust air of 250 m /hr, the clean air device transferred 1,910 m of clean air into the room, which corresponded to a particle concentration of x 10810 -=314 partioles/1 of air. 1,910 With the Royco particle counter, from 70 to 500 particles were counted/1.

Claims (5)

1. CLAIMS:1. A device for ventilating and cleaning air in a room, comprising a casing having an inlet grid and an outlet grid and two other openings, and a preliminary filter, a blower and a high efficiency particulate air filter unit (HEPA filter unit) as hereinbefore defined mounted within the casing, the arrangement being such that in operation air enters the device through the inlet grid from the room and through one of the two other openings referred to from the atmosphere outside the room, passes through the preliminary filter, the blower and the HEPA filter unit in that order, and part of the resulting air is circulated through the outlet grid to the room and part is returned to the atmosphere outside the room through the second opening.

2. A device as claimed in Claim 1, wherein at least One of the grids is constructed as heat exchanger.

3. A device as claimed in Claim 1 or Claim 2, wherein each opening to the atmosphere outside the room is provided with a throttle valve.

4. A device for ventilating and cleaning air in a room, substantially as described herein with reference to, and as illustrated by, the accompanying drawing.

5. A device as claimed in any one of Claims 1 to 4, wherein one of the other openings referred to is between the inlet grid and the preliminary filter, and the other is between the HEPA filter unit and the outlet grid.